If Duch were released he could be harmed both by "accomplices wishing to silence him and by the relatives of victims seeking revenge", Robert Petit, a prosecutor from Canada, told the court.

He added that Duch could seek to leave the country if he was set free in order to escape justice.

Duch's lawyers say their client has promised to co-operate fully with the tribunal.

Duch was arrested in 1999 and charged last year by the tribunal with crimes against humanity.

During the Khmer Rouge's four years in power he ran its secret police as well as the notorious S-21 torture and interrogation centre.

Some 17,000 people are thought to have passed through the centre, with only a handful surviving.

Wednesday marked the second day of the hearing, with media, Khmer Rouge survivors and relatives of their victims again crowding the tribunal building on the outskirts of Phnom Penh.

Duch is one of five former senior Khmer Rouge leaders currently in detention awaiting trial before the tribunal.

Among the five he is the lowest ranking member of the former regime, but his role in charge of the S-21 interrogation centre, housed in a former Phnom Penh high school, has made him one of the most notorious.

He has insisted he was simply following orders from the top to save his own life.

"I was under other people's command, and I would have died if I disobeyed it," he told a government interrogator after his arrest.

The first formal trials for former Khmer Rouge officials and leaders are expected to get under way early next year.

Factfile: Kaing Guek Eav (Duch)

Born in the early 1940s, Duch trained as a teacher before joining the Khmer Rouge

During Khmer Rouge rule between 1975 and 1979 he headed the regime's Santebal secret police

He also headed the notorious S-21 torture and interrogation centre in a former Phnom Penh high school

Prosecutors say Duch's name appears on dozens of execution warrants

Duch fled Phnom Penh when Vietnamese forces invaded in early 1979

Living in a remote jungle hideout, he converted to Christianity in 1996

In 1999 he was arrested and charged with murder, torture and membership of an outlawed group

In 2007 Duch became the first suspect brought before the UN-backed tribunal to try former Khmer Rouge officials